<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  
  <button class="btn">随机数</button>

  <script>
    
    // 1.定义的数组
    const values = [100, 300, 500, 800, 1000]

    // 2.监听按钮的点击
    const btnEl = document.querySelector(".btn")
    btnEl.onclick = function() {
      let currentValue = Math.floor(Math.random() * 1500)
      matchIndex(currentValue)
    }

    // 3.封装函数: 根据value去匹配索引
    function matchIndex(currentValue) {
      // 核心代码
      let currentIndex = values.length - 1

      for (let i = 0; i < values.length; i++) {
        const value = values[i]
        if (value > currentValue) {
          currentIndex = i - 1
          break
        }
      }
      if (currentIndex === -1) return
      console.log("value:", currentValue, "index:", currentIndex)
    }

  </script>
</body>
</html>